Similarly, western bird species such as the western flycatcher and the western tanager are at the eastern limits of their range in the Black Hills; they share habitats with eastern bird species, such as the ovenbird and indigo bunting.

The thickly grassed hillside sloped down in front of me to a belt of forest from which rose the golden, leisurely chiming of the wood thrushes, chanting their vespers; through the still air came the warble of vireo and tanager; and after nightfall we heard the flight song of an ovenbird from the same belt of timber.

As well as helping assess populations of cryptic bird species such as the ovenbird, the new technique might be applied to measuring hard-to-reach populations of marine mammals, such as whales and dolphins.